1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+342!.3-)33)/. G0G03).!,).G0G0!.$G0G037)4#().(b) that there is a requirement for a multiplexing scheme for the interworking between two networks whereboth use non-envelope structured d
2、ata,unanimously declares the viewthat the following fundamental parameters shall be used between networks using no envelope structures.1 Gross bit rateFor transmission on the international link the aggregate bit stream shall have a gross bit rate of 64 kbit/s.2 Tributary channel bit ratesThe followi
3、ng tributary channel bit rates are supported:- 2.4 kbit/s- 4.8 kbit/s- 9.6 kbit/s- 19.2 kbit/sOther bit rates are not excluded.3 Multiplex schemeThe multiplex scheme is shown in Figure 1/X.58. The frame length is 640 bit. The frame duration is 10 ms.Tributary channel data is grouped in octets and ap
4、pears in slots An through Fn. Slots Sn contain synchronization octets.Slots Tn contain service octets.2 Fascicle VIII.3 - Rec. X.583.1 Data octetsOne frame contains 72 data octets. Thus the multiplex stream can cupport24 channels of 2.4 kbit/s, or12 channels of 4.8 kbit/s, or6 channels of 9.6 kbit/s
5、, or3 channels of 19.2 kbit/s, orcombinations thereof.The allocation of individual octets to a tributary channel is detailed below.3.1.1 2.4 kbit/s2.4 kbit/s tributary channels employ 1 out of 24 data octets. A 2.4 kbit/s channel will thus be allocated to allslots with the same identifier, i.e. iden
6、tification letter and identification digit (e.g. A1).3.1.2 4.8 kbit/s4.8 kbit/s tributary channels employ 1 out of 12 data octets. A 4.8 kbit/s channel will thus be allocated to allslots with the same identification letter in the range A-F and two different identification digits 1 and 3 or 2 and 4 (
7、e.g.B1 and B3).3.1.3 9.6 kbit/s9.6 kbit/s tributary channels employ 1 out of 6 data octets. A 9.6 kbit/s channel will thus be allocated to allslots with the same identification letter in the range A-F and four different identification digits 1, 2, 3 and 4 (e.g. D1,D2, D3 and D4).3.1.4 19.2 kbit/s19.
8、2 kbit/s tributary channels employ 1 out of 3 data octets. A 19.2 kbit/s channel will thus be allocated to allslots with two different identification letters from the range A-F: A and D or B and E or C and F, and four differentidentification digits 1, 2, 3 and 4 (e.g. C1, F1, C2, F2, C3, F3, C4 and
9、F4).3.1.5 Other bit ratesFor other bit rates no allocation of octet, to a tributary channel is specified. From the scheme in Figure 1/X.58it can be derived that any bit rate n times 2.4 kbit/s where n is 1 through 24 can be supported. Detailed allocationschemes should be specified by bilateral agree
10、ment.Fascicle VIII.3 - Rec. X.58 33.2 Synchronization octetsOne frame contains 4 synchronization octets. These contain fixed bit patterns as follows:S1 = 27 = 00100111S2 = 1B = 00011011S3 = 05 = 00000101S4 = 35 = 001101013.3 Service octetsThe octets T1 through T4 are available for housekeeping infor
11、mation signals.The following allocation is recommended but not mandatory.Octet T1 contains eight bits, A, B, C, D, E, F, G and H (cf. Recommendation X.50). Bit A is the first bittransmitted.The bit A is used to convey to the distant end alarm indications detected at the local end corresponding to:-
12、absence of incoming pulses,- loss of frame alignment,and that bit A shall be assigned such that:- A equals 1 means no alarm,- A equals 0 means alarm.The other bits B, C, D, C, F, G and H are reserved to convey further international housekeeping signals. Theexact use is under study. Pending the resul
13、t of the study these bits shall be set to binary 1.The octets T2 through T4 are reserved for national use and shall be set to binary 1 on an international link.4 Frame synchronizationFrame synchronization is obtained by the receiving multiplexer during normal operation. No interactionbetween multiplexers at both ends of the link is required for this purpose.
